That day, the inconvenience of blurry vision and sun sensitivity versus a manual exam was well worth the savings.

A few years ago when I was new to Houston and selected a dentist, the hygienist - before looking in my mouth - asked if I wanted a rinse to check for oral cancer. Again, I had the presence of mind to inquire about whether this screening was covered by my insurance. It was not. In fact, it was 60 bucks.

Preventive health care upselling gives consumers options for tests and treatments they may want or need, but will cost extra if you're otherwise covered by insurance.

That's why it's important to know what's covered before the appointment and always remember to ask whether something that's offered will be an out-of-pocket charge.

The U.S. Preventive Services Task Force provides a guide to clinical preventive services that medical professionals should discuss with patients based on gender, age and pregnancy status. (The full report is available on the Houston Advocate blog.) Letter grades are assigned to indicate a recommendation's strength. A and B grades mean a high or moderate certainty of benefit and clinicians are encouraged to routinely offer or provide the service. C grades mean the recommendations may be beneficial to patients in certain populations. A service rated with a D is discouraged because it has no benefit or the harm outweighs the benefit. A service receives an I if the task force concludes that current evidence is insufficient to assess its balance of benefits and harms. (Oral cancer is real, but rare. A screening recommendation is in the early stages of the task force's review and has no letter grade.)

Time also a factor

In the end, only a patient and his or her clinician can determine the value of a specific service.

"You definitely want to be paying for things that have a personal benefit," said Houston health economist Vivian Ho, an economics professor at Rice University who said she's had the retina scan.

"It's impossible to work when your eyes are dilated. I didn't mind paying because I also have a flexible spending account," she said. "And it's a time benefit, but you have to go by the guidance of experts. Ask your health care provider: Why are you saying I should get this?"

Ho also reminds consumers that many medical professionals are also business people who have incentives to make more money.

"If it's at their discretion to recommend tests, then some of them are going to do that - especially if it costs them less than what they receive from the patient or the insurance company. They aren't doing anything unethical to me, they're just acting as economic agents."

Ho, who also is a professor at Baylor College of Medicine, said she personally prefers university-affiliated providers because they teach and research. She added that she values personal recommendations from patients over online ratings of medical professionals.

Affordable Care Act

It's also important to note that the Affordable Care Act, also known as "Obamacare," now requires insurance companies to fully cover a range of preventive services, supplies and screenings without consumers providing co-payments, co-insurance or a deductible.